feat: 增加镜像 arm64 原生构建

[qinhn525]

• ## Summary

• Update the Images workflow to build Docker images for both linux/amd64 and linux/arm64.
• Use GitHub-hosted native ARM runners (ubuntu-24.04-arm) for arm64 image builds.
• Push per-architecture images by digest on non-PR events, then merge them into multi-arch manifest lists for
  the existing GHCR tags.
• Keep PR image jobs as build-only checks with push: false.

Testing

Not yet verified by an actual GitHub Actions run on ubuntu-24.04-arm; this PR should validate that path
through the pull_request workflow.

Checklist

• Documentation updated when behavior or configuration changed.
• Tests added or updated for user-visible behavior.
• No secrets, private endpoints, internal certificates, or local runtime state included.